/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    int maxDepth(TreeNode* root) 
    {
        if(root == NULL)
            return 0;
        int left = maxDepth(root->left);
        int right = maxDepth(root->right);
        return left >= right ? left+1 : right+1;
    }
};